There are many neurological procedures which require the accurate placement of a neurological instrument, including for biopsy, radioactive seed placement, and lesion generation. One of the most common neurological procedures requiring accurate placement is a ventriculostomy procedure in which a cerebral ventricle drain or shunt is installed. Such a drain or shunt is utilized for ventricular drainage when a patient manifests hydrocephalus resulting from congenital brain malformations, acute or chronic infections, tumors, intraventricular hemorrhage, or normal pressure hydrocephalus.
Conventional procedures for the placement of ventricular drains or shunts rely heavily on the skill of the neurosurgeon, and/or are relatively expensive and time consuming. After a CT scan, or other imaging, the neurosurgeon forms a burr hole in the skull, and then the neurosurgeon guides a catheter through the burr hole toward landmarks on the opposite side of the patient's head. It is necessary that the neurosurgeon be able to completely accurately visualize the internal tomography of the brain when performing this procedure, and it is presumed that the catheter is properly located when the surgeon obtains fluid returned through the catheter. In some circumstances, the neurosurgeon feels it advisable to check the location of the catheter, and for that purpose the patient must be subjected to another CT scan of the brain in order to verify proper location of the catheter. Since each separate, individual, CT scan is expensive, and since the prior art procedures are time consuming both for the neurosurgeon and the anaesthesiologist, there has long been a need for procedures more regularly and inexpensively accurately placing ventricular drain or shunt catheters, which will result in longer shunt patency and decreased morbidity due to shunt malposition.
According to one aspect of the present invention, a stereotactic neurological instrument placement guide is provided that may be utilized in numerous different types of neurological procedures, and which has ideal suitability for use in ventriculostomy procedures. The guide according to the invention is simple to construct and to utilize, and can readily enhance accuracy, reduce time, increase confidence, and reduce cost for a given level of confidence, in ventriculostomy procedures and other neurological treatment methods.
The stereotactic guide according to the invention has only first and second skull engaging point members, which have a common central axis. A frame mounts the skull engaging point members for controlled movement with respect to each other along the central axis. Means are provided defining a linear guide passage in the first point member, a straight line extension of the linear guide passage extending along a common central axis, and the linear guide passage is large enough for the passage of a neurological instrument (e.g. catheter or shunt) through it. The termination of the first point member coaxial with the linear passageway and common central axis provides for stabilizing the first point member in a burr hole; for example the termination may comprise a truncated cone.
The point members may be attached to arms, which in turn are attached to a guide sleeve and a guide element (bar or rod) which are movable with respect to each other. A locking screw can lock them in a position to which they have been moved, or they may be biased toward each other by an elastic band, spring loading, or the like. The means defining a linear passage may comprise a slotted sleeve rigidly fixed to the frame arm, with a slotted tubular element received within the sleeve and rotatable from one position in which the slots of the sleeve and tubular member are not aligned, to a second position in which the slots are aligned. When the slots are not aligned, the guide passage is closed and provides positive guiding of the catheter therethrough. When the slots are aligned, the placement guide may be removed from contact with the patient's skull, and the catheter.
According to the present invention, the key to proper utilization of the stereotactic neurological instrument placement guide is the proper location of the fixing point on the opposite side of the patient's skull from the burr hole. The positive location of the fixing point, which will receive the second point member of the placement guide, opposite the proposed site for the burr hole is determined utilizing a CT scan, magnetic resonance imaging (MRI), or another type of coordinate multiplanar tomographic imaging of the patient's skull. Utilizing X, Y, and Z coordinates for the burr hole (marked by a nipple marker or the like), and determining the coordinates of the particular portion of the ventricle, or other location within the brain, desired to be acted upon by the neurosurgeon, the data from the imaging can be used to calculate the loci of points along a straight line between the burr hole and the target area, which loci can be extended to the patient's skull on the opposite side thereof from the burr hole, and that part of the patient's skull can be marked with a nipple marker, oil, or the like. The calculations are preferably provided by vector parameterization, utilizing a programmable scientific calculator, and the gantry angle of the imaging equipment can be automatically accommodated.
Desirably the distance of the target point from the burr hole is also calculated according to the invention, so that the neurosurgeon can use indicia on the catheter to determine when the catheter has been inserted the distance necessary to properly position it at the target. Practicing the method according to the invention, since the placement of the fixing point is accurately determined, there is no necessity for a second CT scan, or the like.
While the invention will be described herein primarily with respect to ventriculostomy procedures, it is to be understood that both the apparatus and procedures according to the invention may be applied to a wide variety of neurological practices. In fact, the basic positioning facilitating features according to the invention are applicable not just to neurosurgery, but in general to determining the position of a line between two points on or within a human patient's body utilizing data normally determined from a coordinate multiplanar tomographic imaging (CT, MRI, etc.) of the patient's body during which the patient is disposed at an angle, and is incrementally advanced between images. Utilizing the present invention it is possible to practice procedures not heretofore contemplated, or to maximize the accuracy of present procedures, since according to the invention it is possible to accurately locate and determine the coordinates of two or more points on or within a human body (e.g. within the brain).